Question: Solve for $p$ : $p + 13 = 28$
Solution: Subtract $13$ from both sides: $ \begin{eqnarray} \\ p + 13 &=& 28 \\ \\ {-13} && {-13} \end{eqnarray} $ $ \begin{eqnarray} \hphantom{13 + p} &\hphantom{=}& \hphantom{28} \\ p &=& 28 {- 13} \\ \end{eqnarray} $ Simplify. $ p = 15$